1. Technical Field
The present invention relates generally to a LED lamp, and more particularly to a dimmable LED lamp, luminance of which could be changed with different voltages provided to the LED lamp.
2. Description of Related Art
Fluorescent lamps are the commonest device for indoor lighting. In order to provide a room with different luminance, a conventional method is to light different numbers of fluorescent lamps since each fluorescent lamp can be turned on and off only, and there is no intermediate status in between. Sometimes, such method leads to uneven brightness in the room when fluorescent lamps at specific locations are off. Furthermore, only a few grades of luminance can be selected because the on/off combinations of fluorescent lamps in a room are limited. In addition, a fluorescent lamp is driven by alternate current (AC) to emit light, and therefore it inevitably flashes, which could cause eyestrain or even eyesight damage.
Therefore, light emitting diode (LED) gradually replaces fluorescent lamps in illumination systems because of its environmental friendliness and its better performance in electro-optical conversion. And since LED is driven by direct current (DC), it doesn't flash, which is another advantage over fluorescent lamps. However, the conventional LED lamps emphasis on keeping stable luminance as voltage fluctuates, which means adjusting the luminance of LED lamps in a DC system is still a problem unresolved.